The present invention relates to a metrologic methodology and instrumentation, in particular to laser-frequency-domain infrared photothermal radiometry (henceforth referred to as FD-PTR or simply PTR) and frequency-domain luminescence (henceforth referred to FD-LM, or simply LM), for detection of dental defects and caries intraorally.
In recent years rapidly increasing research activities have been reported centered on laser induced dc luminescence generated by a continuously (uninterrupted) illuminating optical source as a probing technique for the detection and quantification of physical and chemical processes associated with carious dental enamel. In general, dc luminescence suffers from low signal levels and thus in most cases dyes are used to enhance sensitivity [V. D. Rijke and J. J ten Bosch, xe2x80x9cOptical quantification of caries like lesions in vitro by use of fluorescent dyexe2x80x9d, J. Dent. Res. 69, 1184-1187 (1990)]. Under laboratory conditions, the results appear satisfactory, yet the use of dyes makes the method difficult for clinical applications. Another promising approach is laser-scanned dc fluorescence (or dc luminescence). This technique can detect early carious lesions [J. Baron, K. Zakariasen and B. Patton, xe2x80x9cDetecting CO2 laser effects by 3D image scanned laser fluorescencexe2x80x9d, J. Dent. Res. 72, special issue #1060, 236 (1993);] by producing surface images which are subsequently enhanced via standard image processing techniques [C. D. Gonzalez, K. Zakariasen, D. N. Dederich and R. J. Pruhs, xe2x80x9cPotential preventive and therapeutic hard tissue applications of CO2 and Nd:YAG and Argon lasers in dentistry: A reviewxe2x80x9d, J. Dent. Child May-June, 196-207 (1996)]. Nevertheless, the relatively low SNR limits the contrast and the diagnostic ability of dc laser fluorescence.
There have been three patents issued directed to methods involving dc laser luminescence. (R. R. Alfano, U.S. Pat. No. 4,290,433, Sep. 22, 1981; R. Hibst et. al., U.S. Pat. No. 5,306,144, Apr. 26, 1994; R. Hibst et. al. U.S. Pat. No. 6,024,562, Feb. 15, 2000). The last of these patents makes reference to using periodically modulated (chopped) radiation as a means to eliminating (xe2x80x9cquasi-filtering outxe2x80x9d) the background environmental light interference from the illuminated tooth. A suitable chopping frequency is advised, so as not to coincide with the power-line oscillation frequency. It should be noted that the idea of background light-filtering through modulation described in the patent by R. Hibst et al., neither in spirit, nor in practice does it lead those skilled in the art to our method of providing frequency-scanned amplitude and phase signals of modulated (ac) luminescence as a dental diagnostic means in their own right, where the frequency behavior of the LM signal is used to deduce dynamic optical and photothermal properties of the irradiated region, including scanning imaging.
The technique disclosed in U.S. Pat. No. 5,306,144 issued to R. Hibst et. al., and U.S. Pat. No. 6,024,562 issued to R. Hibst et. al. relies upon long lived fluorescence present in carious regions of the tooth that only emits in the red spectral region. This decay time and spectral characteristics are typical of metal free porphyrin monomers (Konig, K., Schneckenburger, H., Hibst, R., xe2x80x9cTime-gated in vivo autofluorescence imaging of dental cariesxe2x80x9d, Cell Mol. Biol., 1999, March, Volume 45, #2, pages 233-239). The spectral characteristics were found to be typical of protoporphyrin IX, which may be present due to bacterial biosynthesis occurring within carious tissue (Konig, K., Flemming, G., Hibst, K., xe2x80x9cLaserxe2x80x94induced autofluorescence spectroscopy of dental cariesxe2x80x9d, Cell Mol. Biol., 1998, December, Volume 44, #8, pages 1293-1300). There is also speculation that pigments present in specific foods or drink may be responsible (Longbottom, C., xe2x80x9cCaries detectionxe2x80x94Current status and future prospects using lasersxe2x80x9d, in Lasers in Dentistry VI, Featherstone, J. D. B., Rechmann, P., Fried, D., Proceedings of SPIE, 2000, Volume 3910, pages 212-218). This is a much different approach to finding carious regions than the invention disclosed in the present patent.
A variety of methods have been developed for using lasers to treat carious tooth structures. Yessik et al. (U.S. Pat. No. 5,621,745 Apr. 15, 1997) describes one method of using a modulated pulsed laser to remove carious tooth material. Kowalyk (U.S. Pat. No. 5,281,141, Jan. 25, 1994) describes a method for using a Nd:YAG laser to treat and remove carious tooth material.
A number of laser systems have been proposed for curing or setting composite resins that are used to directly restore teeth. These resins are placed into cavity preparations that encompass the defects in the tooth or the carious regions of the tooth. Kowalyk (U.S. Pat. No. 5,281,141, January 1994), Kowalyk et al. (U.S. Pat. No. 5,456,603, October 1995), Levy (U.S. Pat. No. 5,885,082 March 1999) and Cipolla (U.S. Pat. No. 5,616,141 April 1997) disclose several techniques for curing or acting as a catalyst for the curing of light cured or dual cured dental composites. Issues such as polymerization shrinkage of the composite resin from the cavity or tooth walls are still being examined (Cobb, D S., et al. xe2x80x9cPhysical properties of composite cured with conventional or argon laserxe2x80x9d, Am. J., 1996, October, Volume 9, No. 5, pages 199-202), (Tarle et al. xe2x80x9cThe effect of photopolymerization method on the quality of resin samplesxe2x80x9d, J. Oral Rehabil., 1998, June, Volume 25, No. 6, pages 436-442). Laser systems may be utilized in the photopolymerization of composites, but heat generation and marginal integrity of the restoration still need to be examined.
Frequency-Domain Photothermal Radiometry (FD-PTR) is a growing technology for the nondestructive evaluation (NDE) of sub-surface features in opaque materials [M. Munidasa, T. C., A. Mandelis, S. K. Brown, and L. Mannik, xe2x80x9cNon-destructive depth profiling of laser processed Zr-2.5Nb alloy by infrared photothermal radiometryxe2x80x9d, J. Mat. Sci. Eng. A 159, 111-118 (1992), G. Walther, xe2x80x9cPhotothermal nondestructive evaluation of materials with thermal wavesxe2x80x9d in Progress in photothermal and photoacoustic science and technology, A. Mandelis, ed., Vol. 1, pp. 205-298 Elsevier, N.Y. (1992)]. It has also shown promise in the study of excited-state dynamics in active optically transparent solid-state (laser) materials [A. Mandelis, M. Munidasa, and A. Othonos, xe2x80x9cSingle-ended infrared photothermal radiometric measurements of quantum efficiency and metastable lifetime in solid-state laser materials: the case of ruby (Cr3+:Al2O3)xe2x80x9d, IEEE J. Quant. Electron. 29, 1498-1504 (1993)].
The FD-PTR technique is based on the modulated thermal infrared (blackbody or Planck-radiation) response of a medium, resulting from radiation absorption, non-radiative energy conversion and excited-to-ground-state relaxation, followed by temperature rise and subsequent emission of infrared photons. The generated signals carry sub-surface information in the form of a temperature depth integral. As a result, PTR has the ability to penetrate and yield depth-profilometric information about an opaque medium well below the range of optical imaging. Owing to this ability, pulsed-laser PTR has been extensively used with turbid media such as tissue [A. J. Welch and M. J. C. van Gemert eds., in Optical-thermal response of laser-irradiated tissue, Plenum, N.Y (1995), S. A. Prahl, A. I. Vitkin, U. Bruggemann, B. C. Wilson, and R. R. Anderson xe2x80x9cDetermination of optical properties of turbid media using pulsed photothermal radiometryxe2x80x9d, Phys. Med. Biol. 37, 1203-1217 (1992)] to study the sub-surface deposition localization of laser radiation, a task which is difficult or impossible for optical methods in tissue due to excessive scattering.
Very recently, dental applications of pulsed PTR focused on the diagnostics of dentin and enamel have been reported as disclosed in D. Fried, W. Seka, R. E Glena, and J. D. B. Featherstone, xe2x80x9cThermal response of hard dental tissues to 9- through 11-xcexcm CO2-laser irradiationxe2x80x9d, Opt. Eng. 35, 1976-1984 (1996), D. Fried, S. R. Visuri, J. D. B. Featherstone, J. T. Walsh, W. Seka, R. E. Glena, S. M. McCormack, and H. A. Wigdor, xe2x80x9cInfrared radiometry of dental enamel during Er:YAG and Er:YSGG laser irradiationxe2x80x9d, J. Biomed. Opt. 1, 455-465 (1996). These preliminary studies have examined the temperature behavior of dental tissues, their tolerance to optical-to-thermal energy conversion and deposition, and their ablation threshold by high-fluence pulsed lasers. Unfortunately, the high-fluence deposition and wideband nature of pulsed photothermal detection, coupled with laser-pulse jitter and the high noise content inherent to all broadband thermal (incoherent) signal techniques, prohibits the non-destructive application of this PTR mode to dental imaging, at least in competition with dc luminescence and other imaging diagnostics.
In contrast, FD-PTR, on the other hand, exhibits much higher signal-to-noise ratio (SNR) than its pulsed counterpart [A. Mandelis, xe2x80x9cSignal-to-noise ratios in lock-in amplifier synchronous detection: A generalized communications systems approach with application to frequency-, time-, and hybrid (rate-window) photothermal measurementsxe2x80x9d, Rev. Sci. Instrum. 65, 3309-3323 (1994)] and a fixed probed depth with the use of a single modulation frequency. Therefore, it would be very advantageous to provide a method of dental imaging based on FD-PTR.
The present invention provides a method with frequency-domain infrared photothermal radiometry (FD-PTR) and modulated laser luminescence (FD-LM), as complementary dynamic dental diagnostic tools, for quantifying sound and defective (cracked, carious) teeth intraorally.
In one aspect of the invention there is provided a photothermal radiometric and luminescence method for inspection of teeth, comprising the steps of:
irradiating a portion of a surface of a tooth with a light source emitting at an effective wavelength wherein photothermal radiometric signals and luminescence signals are responsively emitted from said portion of the tooth;
detecting said emitted photothermal signals and said luminescence signals;
demodulating said emitted photothermal signals into photothermal phase and amplitude components and said luminescence signals into luminescence phase and amplitude signals; and
comparing said photothermal phase and amplitude signals to photothermal phase and amplitude signals of a reference sample and comparing said luminescence phase and amplitude signals to luminescence phase and amplitude signals of a reference sample to determine differences between said portion of said tooth and said reference sample and correlating said differences with defects in said tooth.
The present invention also provides a simultaneous photothermal radiometric and luminescence method for imaging of a tooth surface and detection of the tooth defects intraorally, comprising the steps of:
scanning a tooth surface intraorally by irradiating the tooth surface with a light source at fixed frequency wherein a photothermal radiometric signals and luminescence signal is responsively emitted from said tooth;
detecting said emitted photothermal radiometric signals and said luminescence signals;
demodulating said emitted photothermal radiometric signals into photothermal phase and amplitude signals and said luminescence signals into luminescence phase and amplitude signals using a lock-in amplifier and normalizing said demodulated photothermal phase and amplitude signals and normalizing said demodulated luminescence phase and amplitude signals to cancel light source fluctuations and lock-in amplifier dependencies; and
comparing said normalized photothermal phase and normalized amplitude signals to photothermal phase and amplitude signals of a reference sample and comparing said normalized luminescence phase and normalized amplitude signals to luminescence phase and amplitude signals of a reference sample to determine differences between said portion of said tooth and said reference sample thereby identifying defects in said tooth.
In another aspect of the invention there is provided a device for photothermal radiometric and luminescence for inspection of teeth, comprising the steps of:
a light source for irradiating a portion of a surface of a tooth with an effective wavelength wherein photothermal radiometric signals and luminescence signals are responsively emitted from said portion of the tooth;
detection means for detecting said emitted photothermal signals and said luminescence signals;
demodulating means for demodulating said emitted photothermal signals into photothermal phase and amplitude components and said luminescence signals into luminescence phase and amplitude signals; and
processing means for comparing said photothermal phase and amplitude signals to photothermal phase and amplitude signals of a reference sample and comparing said luminescence phase and amplitude signals to luminescence phase and amplitude signals of a reference sample to determine differences between said portion of said tooth and said reference sample and correlating said differences with defects in said tooth.
In this aspect of the invention the light source may be a laser emitting in the near-ultraviolet, visible or near-infrared spectral ranges and the demodulation means may be a lock-in amplifier. In this aspect of the invention the device may include a laser for treatment of defects.